70 
LIFE, IN IIS LOWER FORMS. 
pleasure of the animal, or under the stimulus of pressure, 
the thread is shot forth from one end of the cell with great 
force, until it extends to a length from twice to fifty times 
that of the cell. When fully extended, it is seen that the 
thread is but a continuation of the cell itself; that when it 
was dormant, it was turned in ; and that in the process of 
expulsion, every part of its length has actually been turned 
inside out, like the finger of a glove. Sometimes the 
thread appears simple, but in those cases in which a cham- 
ber appeared within the cell, it is furnished with an 
armature of barbed threads, which after expulsion pro- 
ject from the sides of the thread in various directions. 
The propulsion of the thread is sufficiently forcible to 
enable it to enter the tissues of other animals, and the 
barbed structure enables the weapon to retain its hold in 
the flesh, which facts warrant the presumption that a 
highly poisonous fluid is at the same time injected, capable 
of arresting and destroying animal life. Some of the forms 
of these organs are represented in the accompanying 
figures. 
In captivity, the process of taking food may be witnessed 
